In recent years, wearable devices have been developed progressively with the spread of Internet of Things (IoT). Representative examples thereof include a watch and glasses that can be connected with internet. Wearable devices that can always monitor physical conditions are also necessary in a medical field and a sports field, and are expected to be a growth field in the future.
Wearable devices include a form that is adhered to a body to monitor physical conditions constantly. Such a wearable device is generally composed of a bio-electrode to detect electric signals from a body, wiring to send the electric signals to a sensor, a semiconductor chip to be the sensor, and a battery. Normally, an adhesive pad is necessary to be adhered to skin. The structures of a bio-electrode, wiring around the same, and an adhesive pad are specifically described in Patent Literature 1. In the wearable device described in Patent Literature 1, a silicone based adhesive film is disposed around the bio-electrode, and the bio-electrode is connected with a sensor device by stretchable silver wiring in the shape of bellows coated with a stretchable urethane film.
Urethane films have high stretchability and strength to possess excellent mechanical properties as coating films for stretchable wiring. The urethane film, however, has hydrolytic properties to cause degradation, thereby inducing a disadvantage of lowering the stretchability and the strength due to hydrolysis. On the other hand, silicone films are free from hydrolytic properties, but has a disadvantage of lower strength.
Accordingly, it has been conducted to investigate silicone-urethane polymers with each polymer main chain having both of a urethane bond and a siloxane bond. The oared product of this polymer has higher strength than single silicone, and lower hydrolytic properties than single polyurethane. The cured product of this polymer, however, fails to equal the strength of single polyurethane and the repellency of single silicone, only giving strength and repellency in the middle of those of silicone and polyurethane.
On the other hand, a material in which polyurethane and silicone are blended has been investigated. For example, Patent Literature 2 and Patent Literature 3 describe a material in which non-reactive silicone and crosslinkable polyurethane are blended. In a film formed from such a material, silicone comes up to the surface of a cured polyurethane film (bleed out) to improve the repellency of the film surface. In such a film, however, the silicone is not crosslinked, which causes peeling of silicone on the film surface to be tend to lower the repellency. Additionally, without a surface, the silicone does not come up to the surface of the film. Accordingly, a compression molded material in which the film is sandwiched between sheets does not show high repellency.
Additionally, a diol material has been proposed for synthesizing polyurethane having a siloxane side chain. Patent Literatures 4 and 5 each describe a diol compound for forming polyurethane in which silicone is attached to the side chain. The side chain silicone group shown therein is a linear silicone in which the siloxane terminal is bonded to the diol compound.